Methane is one of the most expensive carbon sources for microbial growth. It is known that there are many microorganisms capable of growing on a culture medium in the presence of methane as the principle carbon source. However, not all of these microorganisms share good growth characteristics. It is also known that methane-grown microorganisms can be used to convert methane to methanol under aerobic conditions.
These methane-utilizing microorganisms are generally known as "methylotrophs". The classification system for methylotrophs proposed by R. Whittenbury et al. (J. of Gen. Microbiology, 61, 205-218 (1970)) is the most widely recognized. In their system, the morphological characteristics of methane-oxidizing bacteria are divided into five groups: Methylosinus, Methylocystis, Methylomonas, Methylobacter and Methylococcus.
Recently, Patt, Cole and Hanson (International J. Systematic Bacteriology, 26, (2) 226-229 (1976)) disclosed that methylotrophic bacteria are those bacteria that can grow non-autotrophically using carbon compounds containing one or more carbon atoms but containing no carbon-carbon bonds. Patt et al. have proposed that methylotrophs should be considered "obligate" if they are capable of utilizing only carbon compounds containing no carbon-carbon bonds (e.g., methane, methanol, dimethylether, methylamines, etc.) as the sole sources of carbon and energy whereas "facultative" methylotrophs are those organisms that can use both compounds containing no carbon-carbon bonds as well as compounds having carbon-carbon bonds as the sources of carbon and energy. In their paper, Patt et al. disclosed a methane-oxidizing bacterium, which they identified as Methylobacterium organophilum sp nov. (ATCC 27,886). This bacterium presumably differs from all previously described genera and species of methane-oxidizing bacteria because of its ability to utilize a variety of organic substrates with carbon-carbon bonds as sources of carbon and energy.
It is now well recognized that there are two types of methylotrophic microorganisms based on their ability to grow on carbon-containing substrates. One type has been referred to as "methane-utilizers" and the other has been referred to as "methanol-utilizers". The methanol-utilizers are unable to grow in the presence of methane as the sole carbon and energy source, but will grow in the presence of methanol, methylamine, etc. The methane-utilizers are capable of growing on a plurality of C.sub.1 -type compounds, including methane, methanol, dimethyl ether, etc. Within the group of methane-utilizing methylotrophs and methanol-utilizing methylotrophs, there are obligate and facultative types of methylotrophic microorganisms. The obligate methane-utilizer type methylotrophic microorganisms will only grow on C.sub.1 -type compounds, e.g., methane, methanol, dimethyl ether, methyl formate, methyl carbonate, etc. The facultative methane-utilizer type methylotrophic microorganisms will not only grow on the above-mentioned C.sub.1 -type compounds, but will also grow on other organic compounds such as glucose. The obligate methanol-utilizer type methylotrophic microorganisms will grow on C.sub.1 compounds, e.g., methanol, methylamine, but not on methane or on organic compounds such as glucose. The facultative methanol-utilizer type methylotrophic microorganisms will grow on the C.sub.1 -type compounds mentioned above (but not methane) and various other organic compounds such as glucose.